The study proposes to measure the mechanical frequency response pattern of the vibrating structures in the cochlea. Complete curves of amplitude and phase vs frequency will be generated for points in all four turns of the guinea-pig cochlea. The instrumentation to be used is a laser interferometer coupled to a special fiber optic probe that preserves the coherence of the light. The fiber is sufficiently small that it will permit operation with minimal surgical disruption of the cochlea. In the initial set of measurements SPL as monitored by a probe at the eardrum will be held constant. However, since the instrumentation also lends itself well to measurement of other vibrating points, eventually stapes amplitude and phase will also be included. Because the resolution of the instrument is a small fraction of an Angstrom the measurements will be made at normal operating levels.